The present invention relates to an electromagnetic rotary actuator, and more particularly to such a rotary actuator for use as an actuator for turning a control rod of a hydraulic damper of the variable damping force type.
EP 0 329 471, which was published on Aug. 23, 1989, discloses a rotary actuator of the above kind. This known actuator comprises a rotor including a support disk of non-magnetic material, rotatable with a shaft normal to its plane, and provided at its periphery with inserts distributed in circular symmetry. These inserts are made from permanent magnetic material and magnetized in a parallel relationship to the shaft in alternately opposite directions. A stator includes a cylindrical casing of non-magnetic material having a first end wall and a second end wall. The internal face of the first end wall of the casing is covered with a first annular disk of non-permanent magnetic material carrying coils distributed in circular symmetry. The internal face of the second end wall of the casing is covered with a second annular disk of magnetic material. The support disk includes a central hub arranged between the first and second annular disks and rotatably supported by a first bearing and a second bearing which are arranged adjacent said first and second walls, respectively. This actuator is not satisfactory in that an appreciable mechanical noise is produced when the rotor is attracted by the coils upon supply of alternate electric pulses.
An object of the present invention is to improve the rotary actuator such that the production of such mechanical noise is eliminated.